Scott, in the schematic submitted, can't for the life of me figure out why
the breaker (fuse?) that goes to the gear switch would be connected to the
main bus rather than the down-stream side of the 50 amp pump breaker. The
way it's shown, one would need to pull TWO breakers to positively safe the
system to do a proper emergency gear drop instead of just the one (you want
to de-energize the relays, since they're only for intermittent use, as well
as the main power to the pump circuit in case of a stuck relay, right?).

In addition, there really needs to be a diode added to each relay control
terminal to ground (cathode to the terminal) or the pressure switches and
gear switch contacts will die an early death from the inductive kick when
the current to the relay coil is interrupted, e.g., relay is turned off.
FWIW, the same is true of the starter relay, which is identical to the pump
relays, at least in my airplane.

As a firm proponent of the KISS principal, especially for a system that is
likely to be needed while in a relatively high stress situation, having to
remember to pull just one breaker instead of two seems preferable.

Dan,

 

Note that Bob's "just pull the relay breaker" is fine for testing (assuming the system was wired the Lancair way).  You are right that ultimately one should be able to pull the motor breaker, too.  KISS would imply that the same method used for testing would be used in an emergency.  Remember the construction manual warning about not pulling both breakers.

 

Yes, you are right about the coil diodes (or MOVs, see Bob Nuckoll's Aeroelectric web site) and I have them installed.  It just seemed like there wasn't room on the Lancair diagram for more stuff and I wanted to emphasize the other, more severe issues.

 

KISS works for me.......